Metals have many more empty orbits than electrons available to fill them.
For example, iron requires 5 electrons to fill
its outermost 3d orbital.

Metallically bonded solids share the following properties: low to moderate
hardness, malleability, and ductility (weak delocalized bonds); very good
thermal conductivity and electrical
conductivity (free electrons in cloud); and form crystals with high symmetry
(nuclei pack well).